Optical waveguide device

ABSTRACT

To obtain a optical waveguide device suppressed in fluctuations of characteristics of optical waveguide element due to temperature changes, hence not requiring temperature adjusting means. An arrayed waveguide grating as a optical waveguide device comprises a flat waveguide element of specified thickness h 0  forming an optical waveguide layer on a silicon substrate, a first correction substrate of thickness h1 adhered to the optical waveguide layer side, and a second correction substrate of thickness h 4  adhered to the silicon substrate side. By properly setting the coefficients of linear expansion α 1 , α 4  and Young&#39;s moduls E 1 , E 4  of the two correction substrates, and using first and second adhesives of high rigidity, warp and expansion and contraction of the waveguide element due to temperature changes can be suppressed to minimum limit. Therefore, the optical waveguide device does not require temperature adjustment.

FIELD OF THE INVENTION

[0001] The present invention relates to a optical waveguide device as afilter device used in optical communications or information processingfield using light, and more particularly to a optical waveguide devicedecreased in the temperature dependence or decreased to a level whichcan be ignored.

BACKGROUND OF THE INVENTION

[0002] Along with the spread of optical communication technology anddevelopment of information processing technology using light, theoptical waveguide devices come to be used widely as filter device. Inthis kind of optical waveguide device realizing various functions bymaking use of interference of light, generally, since the refractiveindex and optical path length vary depending on the ambient temperature,it is characterized by fluctuation of the passing band or centralwavelength.

[0003] Such dependence of central wavelength on temperature in theoptical waveguide is generally expressed in formula (1). $\begin{matrix}{\frac{\lambda_{0}}{T} = {\frac{\lambda_{0}}{n_{eq}} \cdot \left( {\frac{1}{L}\frac{S}{T}} \right)}} & (1)\end{matrix}$

[0004] where λ₀ is the central wavelength, n_(eq) is the equivalentrefractive index of optical waveguide, and 1/L·dsss/dT is thetemperature coefficient of optical path length. The temperaturecoefficient of optical path length can be expressed in formula (2).$\begin{matrix}{{\frac{1}{L}\frac{S}{T}} = {\frac{n_{eq}}{T} + {n_{eq}\alpha}}} & (2)\end{matrix}$

[0005] where α is the thermal expansion coefficient of the opticalwaveguide. The thermal expansion coefficient α can be generallyapproximated by the thermal expansion coefficient of the substratematerial. From these formulas (1) and (2). it is known possible tochange the temperature dependence of the center wavelength of theoptical waveguide device by adjusting the thermal expansion coefficientof the substrate.

[0006] That the optical waveguide device has a temperature dependencemeans that some means is necessary for keeping its characteristicconstant regardless of changes of ambient temperature. As such means,for example, it has been attempted to incorporate a Peltier element orheater in the module. But it requires an extra element or part to beincorporated, and not only the cost of the optical waveguide device orthe module using it is increased, but also it is contradictory toreduction of size or weight. Accordingly, it has been studied to developa new technique for realizing temperature independence, that is,rendering the optical waveguide device a thermal.

[0007] Techniques for lessening the temperature dependence aredisclosed, for example, in Japanese Patent Application Laid-open No.11-174251, Japanese Patent Application Laid-open No. 2000-206348. SignalSociety General Meeting 2000, C-3-13, and Electronics Letters Oct. 12,2000, Vol. 36, No. 21.

[0008]FIG. 1 and FIG. 2 show an optical waveguide element substrate, andspecifically FIG. 1 shows its plane structure, and FIG. 2 shows asection of the substrate cut in the longitudinal direction in FIG. 1.The optical waveguide element substrate 101 of this example composes aMach-Zehnder interferometer, which comprises waveguides 103, 104connected to an input port 102 ₁ and an output port 102 ₂, first andsecond couplers 105, 106 connected to these waveguides 103, 104, andfirst and second gratings 107, 108 disposed parallel between thesecouplers 105, 106.

[0009] In this optical waveguide element substrate 101, as shown in FIG.2, a material of a large thermal expansion coefficient such as aluminumplate 111 is adhered to the reverse side. Due to difference in thethermal expansion coefficient from the aluminum plate 111, a thermaldistortion is generated in the optical waveguide element substrate 101.By this thermal distortion, the optical waveguide layer is warped asshown in FIG. 2, and hence the linear expansion coefficient issuppressed to the negative side, so that the temperature dependence ofthe optical waveguide element substrate 101 is lowered.

[0010] By this technique, however, when the light guiding direction andwarping direction are deviated, polarization dependence occurs.Accordingly, the optical waveguide element substrate to which thistechnique can be applied is limited to the optical waveguide element ofwhich light guiding direction is almost one-dimensional or one directionas shown in FIG. 1. In other words, it cannot be applied to the opticalwaveguide element of which light guiding direction is two-dimensional orX and Y directions. This is explained in the following.

[0011]FIG. 3 shows an optical waveguide element substrate of which lightguiding direction is two-dimensional, presenting an example of AWG(arrayed waveguide grating). The optical waveguide element substrate 121of this example comprises a first waveguide 124 or a second waveguide125 connected to a first port 122 or a second port 123, a first orsecond slab waveguide 126 or 127 having one end connected to the firstoptical waveguide 124 or second optical waveguide 125, and a pluralityof channel waveguide arrays 128 mutually connecting the other ends ofthe slab waveguides 126, 127. The optical waveguide element forcomposing this optical waveguide element substrate 121 has a lightmultiplexing and demultiplexing function, and has a central wavelengthof minimum loss as optical filter characteristic.

[0012]FIG. 4 shows a bimetal structure formed by adhering plates ofdifferent coefficients of thermal expansion to the optical waveguideelement substrate 121 shown in FIG. 3. The optical waveguide elementsubstrate 121 is composed of a silicon substrate 121A, and a waveguidelayer 121B formed on its surface, and a plate material 129 of adifferent thermal expansion coefficient is adhered to the lower side ofthe silicon substrate 121A in order to compose a bimetal structure.

[0013]FIG. 5 compares the central wavelength characteristics as theoptical filter characteristics in relation to the substrate temperaturein the optical waveguide element substrate shown in FIG. 3, having aplate material for composing a bimetal structure adhered and not adheredto the substrate. This example is disclosed, for instance, inElectronics Letters Oct. 12, 2000, Vol. 36, No. 21. In the diagram, twocharacteristic lines 131, 132 refer to a case of the substrate to whicha plate material is not adhered to compose a bimetal structure, andspecifically the characteristic line 131 consisting of black squaresshowing measuring points shows a case of TM polarization, and thecharacteristic line 132 of blank squares indicates a case of TEpolarization. Other two characteristic lines 133, 134 refer to thebimetal structure, and the characteristic line 133 of black circlesshows a case of TM polarization and the characteristic line 134 of whitecircles indicates a case of TE polarization.

[0014] As known from FIG. 5, the bimetal structure is smaller indislocation of the central wavelength with respect to temperature, andshows better results than the non-bimetal structure. In these twocharacteristic lines 133, 134, however, the difference of dislocation ofcentral wavelength when the temperature is low and the difference ofdislocation of central wavelength when the temperature is high are notequal to each other, and a fluctuation occurs in these differences dueto temperature. Therefore, not only the polarization dependence isincreased, but also the temperature dependence is increased.

[0015]FIG. 6 and FIG. 7 show measures for solving such problem. In theproposal presented at Signal Society General Meeting 2000, C-3-13, analuminum plate 142 is adhered to a waveguide substrate 141 shown in FIG.6, and it is processed as shown in FIG. 7. Namely, a region 141A of aspecified width including a waveguide 143 is formed in a convex shapethicker than the other region 141B, and the aluminum plate 142 isremoved at the position corresponding to the waveguide 143.

[0016] Thus, in this proposal, by forming the structure as shown in FIG.7, it is attempted to cancel the distortion occurring vertically in thewaveguide direction. Although such technique is effective in thewaveguide device having the guiding direction limited in one direction,it is difficult to apply in the optical waveguide element of whichguiding direction is two-dimensional such as the optical waveguideelement substrate 121 shown in FIG. 3.

[0017]FIG. 8 shows a proposal of adhesion of a substrate having anegative linear expansion coefficient to the upper surface of theoptical waveguide element. As disclosed in Japanese Laid-open Patent No.10-39150, Japanese Patent Application Laid-open No. 2000-292632,Japanese Patent Application Laid-open No. 11-109155, and Japanese PatentApplication Laid-open No. 2000-352633, as shown in FIG. 8, a substrate151 having a negative linear expansion coefficient is adhered to an AWG152, and the entire linear expansion coefficient is suppressed to thenegative side. The arrayed waveguide grating in the diagram is composedsame as shown in FIG. 13, that is, multiplex lights of wavelengths λ₁,λ₂, . . . λ_(N) are entered from the first port 122 side, and opticalsignals separated into wavelengths λ₁, λ₂, . . . λ_(N) are taken outfrom the second port 123 side.

[0018] On the other hand, FIG. 9 shows other example of adhesion of asubstrate having a negative linear expansion coefficient to the opticalwaveguide element. In this example, at both sides of an opticalwaveguide layer 162 having an optical waveguide pattern 161 and anoptical waveguide substrate 163 disposed at its lower side, materials ofnegative linear expansion coefficient composed of substrates 164, 165having mutually different coefficients of linear expansion are adhered.Such technique is disclosed, for example, in Japanese Patent ApplicationLaid-open No. 11-1099155, and same effects as in the proposal in FIG. 8are obtained.

[0019] Japanese Patent Application Laid-open No. 2000-292632 alsoproposes a Mach-Zehnder interferometer same as shown in FIG. 9. In theproposal disclosed in Japanese Patent Application Laid-open No.2000-292632, however, a first carbon sheet having a negative linearexpansion coefficient in a fibrous texture direction without coveringthe 3 dB coupler is adhered to the waveguide surface for composing theoptical waveguide layer 162, and a second sheet of a similar structureis adhered to the optical waveguide substrate 163 at the reverse side.Using the first and second carbon sheets (corresponding to thesubstrates 164, 165 having mutually different coefficients of linearexpansion in FIG. 9), by weaving and forming a textile sheet, the ratioof the overall thickness of the substrate having negative coefficientsof linear expansion is increased with respect to the thickness of theoptical waveguide layer 162, and the suppressing effect of wavelengthchanges due to temperature is enhanced.

[0020] However, in the technologies disclosed in Japanese PatentApplication Laid-open No. 10-39150, Japanese Patent ApplicationLaid-open No. 2000-292632, and Japanese Patent Application Laid-open NO.11-109155, from the viewpoint of suppressing expansion or contraction ofthe waveguide element due to temperature as much as possible, a materialhaving a negative linear expansion coefficient is adhered to both sidesof the optical waveguide element. Only by adhering the material having anegative linear expansion coefficient to both sides of the opticalwaveguide element, the optical waveguide element is warped due todifference in the linear expansion coefficient, in addition to the warpcaused by expansion or contraction due to temperature.

[0021] Namely, to eliminate the temperature dependence of the opticalcharacteristics of the optical waveguide element, and suppress thethermal deformation of the waveguide element in the longitudinaldirection, hitherto, it has been attempted to adhere a correction platehaving a smaller linear expansion coefficient than the waveguideelement. In such technique, however, bending stress is generated by thedifference in the linear expansion coefficient, and thermal deformationin warping direction occurs, and other optical characteristics of thewaveguide element deteriorate.

[0022] It is hence an object of the invention to present a opticalwaveguide device capable of suppressing fluctuations of thecharacteristics of the optical waveguide element possibly occurring dueto temperature changes, thereby not requiring temperature adjustingmeans.

SUMMARY OF THE INVENTION

[0023] The invention according to claim 1 is a optical waveguide devicewhich comprises (a) a flat waveguide element having a specifiedthickness with a waveguide layer formed on a substrate, and (b) acorrection substrate made of a plurality of flat materials affixed toboth sides or one side of the waveguide element, for decreasing thelength and warping force of the waveguide element due to temperaturechanges as compared with the case of the waveguide element alone.

[0024] Namely, according to the invention of claim 1, plural flatcorrection substrates are affixed to both sides or one side of the flatwaveguide element, and all of them including the waveguide element areset to such values that their length and warping force due totemperature changes may be decreased as compared with the case of thewaveguide element alone. For example, when one correction substrate isaffixed to one side of the waveguide element, warping may occur on thewhole due to difference in the linear expansion coefficient of thewaveguide element, but this warping can be decreased by affixing furtherone or a plurality of correction substrates to this correction substrateand setting the coefficients of linear expansion of these correctionsubstrates at proper values. Moreover, by correcting in the direction ofsuppressing the expansion or contraction due to temperature of thewaveguide element by these correction substrates, fluctuations ofcharacteristics of the waveguide element can be suppressed iftemperature changes occur, so that temperature adjustment of waveguideelement may not be required.

[0025] The invention according to claim 2 is a optical waveguide devicewhich comprises (a) a flat waveguide element having a specifiedthickness with a waveguide layer formed on a substrate, and (b) firstand second correction substrates made of two flat materials affixed toboth sides of the waveguide element, having their coefficients of linearexpansion set at such values as to decrease the length and warping forceof the waveguide element due to temperature changes as compared with thecase of the waveguide element alone.

[0026] Namely, according to the invention of claim 2, first and secondcorrection substrates are affixed so as to enclose at both sides of theflat waveguide element, and the coefficients of linear expansion of thefirst and second correction substrates are set to such values that thelength and warping force of the waveguide element due to temperaturechanges may be decreased as compared with the case of the waveguideelement alone. For example, when the first correction substrate isaffixed to one side of the waveguide element, warping may occur on thewhole due to difference in the linear expansion coefficient of thewaveguide element, but this warping can be decreased by affixing thesecond correction substrate to the opposite side and setting its linearexpansion coefficient to a proper value. Moreover, by correcting in thedirection of suppressing the expansion or contraction due to temperatureof the waveguide element by the first and second correction substrates,fluctuations of characteristics of the waveguide element can besuppressed if temperature changes occur, so that temperature adjustmentof waveguide element may not be required.

[0027] The invention according to claim 3 is a optical waveguide devicewhich comprises (a) a flat waveguide element having a specifiedthickness with a waveguide layer formed on a substrate, and (b) firstand second correction substrates made of two flat materials affixed toboth sides of the waveguide element, having their coefficients of linearexpansion, or moduli of longitudinal elasticity (hereinafter calledYoung's moduli), or thicknesses, or plural items thereof set at suchvalues as to decrease the length and warping force of the waveguideelement due to temperature changes as compared with the case of thewaveguide element alone.

[0028] Namely, according to the invention of claim 3, first and secondcorrection substrates are affixed so as to enclose at both sides of theflat waveguide element, and the coefficients of linear expansion of thefirst and second correction substrates, or Young's moduli, orthicknesses, or plural items thereof set at such values as to decreasethe length and warping force of the waveguide element due to temperaturechanges as compared with the case of the waveguide element alone. Forexample, when the first correction substrate is affixed to one side ofthe waveguide element, warping may occur on the whole due to differencein the linear expansion coefficient of the waveguide element, but thiswarping can be decreased by adhering the second correction substrate tothe opposite side and setting its linear expansion coefficient to aproper value. Or the warping may be decreased by disposing onecorrection substrate at the waveguide layer side of the waveguideelement, and setting the thickness greater than the thickness of thewaveguide element, and setting the linear expansion coefficient largerthan the linear expansion coefficient of the waveguide element, or bysetting the Young's modulus, thickness or plural items thereof at propervalues. Moreover, by correcting in the direction of suppressing theexpansion or contraction due to temperature of the waveguide element bythe first and second correction substrates, fluctuations ofcharacteristics of the waveguide element can be suppressed iftemperature changes occur, so that temperature adjustment of waveguideelement may not be required.

[0029] The invention according to claim 4 is a optical waveguide devicewhich comprises (a) a flat waveguide element having a specifiedthickness with a waveguide layer formed on a substrate, (b) a firstcorrection substrate disposed at the waveguide layer side of thiswaveguide element, having a thickness greater than the thickness of thewaveguide element and a linear expansion coefficient smaller than thelinear expansion coefficient of the waveguide element, and (c) a secondcorrection substrate disposed at the substrate side of the waveguideelement, thicker than the first correction substrate, and having alinear expansion coefficient smaller than the linear expansioncoefficient of the waveguide element and a linear expansion coefficientsmaller than the linear expansion coefficient of the first correctionsubstrate.

[0030] Namely, according to the invention of 4, first and secondcorrection substrates are affixed so as to enclose at both sides of theflat waveguide element. Herein, the second correction substrate isdisposed at the substrate side of the waveguide element, and is thickerthan the first correction substrate, and has a linear expansioncoefficient smaller than the linear expansion coefficient of thewaveguide element, and a linear expansion coefficient smaller than thelinear expansion coefficient of the first correction substrate. Sincethe first and second correction substrates have a thickness greater thanthe thickness of the waveguide element and a linear expansioncoefficient smaller than the linear expansion coefficient of thewaveguide element, expansion or contraction of the waveguide element dueto temperature changes can be suppressed. Moreover, since thesecorrection substrates are enclosing the both sides of the waveguideelement, by properly setting their coefficients of linear expansion orthickness, generation of warp of waveguide element can be suppressed toa minimum limit. In the invention of claim 4, still more, since thefirst and second correction substrates differ in the linear expansioncoefficient and the first correction substrate has a greater negativevalue, the first correction substrate disposed at the waveguide layerside of the waveguide element can be formed relatively in a smallerthickness. In addition, by the first and second correction substrates,expansion and contraction of the waveguide element due to temperaturecan be corrected in a suppressing direction, and fluctuations ofcharacteristics of the waveguide element can be suppressed iftemperature changes occur, so that temperature adjustment of waveguideelement may not be required.

[0031] The invention according to claim 5 is a optical waveguide devicewhich comprises (a) a flat waveguide element having a specifiedthickness with a waveguide layer formed on a substrate, (b) a firstcorrection substrate disposed at the waveguide layer side of thiswaveguide element, having a thickness greater than the thickness of thewaveguide element and a negative linear expansion coefficient, and (c) asecond correction substrate disposed at the substrate side of thewaveguide element, thicker than the first correction substrate, andhaving a negative linear expansion coefficient, and a linear expansioncoefficient of greater absolute value than the linear expansioncoefficient of the first correction substrate.

[0032] Namely, according to the invention of claim 5, first and secondcorrection substrates are affixed so as to enclose at both sides of theflat waveguide element. Herein, the first correction substrate isdisposed at the substrate side of the waveguide element, and is thickerthan the waveguide element, and has a negative linear expansioncoefficient. The second correction substrate is disposed at thesubstrate side of the waveguide element, and is thicker than the firstcorrection substrate, and has a negative linear expansion coefficient,and more specifically has a linear expansion coefficient of a greaterabsolute value than the linear expansion coefficient of the firstcorrection substrate. Since the first and second correction substrateshave a thickness greater than the thickness of the waveguide element anda negative linear expansion coefficient, expansion or contraction of thewaveguide element due to temperature changes can be suppressed.Moreover, since these correction substrates are enclosing the both sidesof the waveguide element, by properly setting their coefficients oflinear expansion or thickness, generation of warp of waveguide elementcan be suppressed to a minimum limit. In the invention of claim 5, stillmore, since the second correction substrate has a linear expansioncoefficient of a larger absolute value than the linear expansioncoefficient of the first correction substrate, the first correctionsubstrate disposed at the waveguide layer side of the waveguide elementcan be formed relatively in a smaller thickness. In addition, by thefirst and second correction substrates, expansion and contraction of thewaveguide element due to temperature can be corrected in a suppressingdirection, and fluctuations of characteristics of the waveguide elementcan be suppressed if temperature changes occur, so that temperatureadjustment of waveguide element may not be required.

[0033] The invention according to claim 6 relates to the opticalwaveguide device of any one of claims 2 to 5, in which one of the firstand second correction substrates is a plate for holding the waveguideelement.

[0034] Namely, according to the invention of claim 6, one of the firstand second correction substrates can be shared by the holding plate ofthe waveguide element.

[0035] The invention according to claim 7 relates to the opticalwaveguide device of claim 3, in which the first and second correctionsubstrates are mutually equal in the linear expansion coefficient andmodulus of longitudinal elasticity, and also mutually equal in thethickness.

[0036] Namely, according to the invention of claim 7, as far as thewaveguide layer itself is not basically warped in spite of temperaturechanges, the first and second correction substrates as the correctionsubstrates disposed at both sides may be composed identically. In thiscase, by setting their coefficients of linear expansion and Young'smoduli at the values for correcting the expansion or contraction of thewaveguide element due to temperature changes, the waveguide element ismade independent of temperature.

[0037] The invention according to claim 8 relates to the opticalwaveguide device of any one of claims 1 to 5, in which the waveguideelement and the correction substrate are affixed to each other with anadhesive of high rigidity.

[0038] Namely, according to the invention of claim 8, when the waveguideelement and correction substrate are affixed with an adhesive of highrigidity, expansion or contraction of correction substrate due totemperature can be efficiently transmitted to the waveguide element, andthe degree of expansion or contraction of waveguide element can bedecreased.

[0039] The invention according to claim 9 relates to the opticalwaveguide device of any one of claims 1 to 5, which further comprises(a) a fiber array for coupling optically with the waveguide element, and(b) a clamp glass disposed at the upper side of the waveguide elementfor reinforcing the adhesive strength of the fiber array.

[0040] Namely, according to the invention of claim 9, the opticalwaveguide device is such a type as to dispose a clamp glass for adheringand reinforcing the fiber array.

[0041] The invention according to claim 10 relates to the opticalwaveguide device of claim 9, in which the thickness of the firstcorrection substrate is equal to or smaller than that of the clampglass.

[0042] Namely, according to the invention of claim 10, attention is paidto the thickness of the entire device when the first correctionsubstrate is disposed at the waveguide layer side of the waveguideelement. The first correction substrate is as thin as the clamp glass orless, and the thickness of the entire device is not particularlyincreased.

[0043] The invention according to claim 11 relates to the opticalwaveguide device of any one of claims 1 to 5, in which at least one ofthe confronting surfaces of the waveguide element and correctionsubstrate is a course surface.

[0044] Namely, according to the invention of claim 11, since at least apart of the confronting sides of the waveguide element and correctionsubstrate is a coarse surface, expansion or contraction of correctionsubstrate due to temperature can be efficiently transmitted to thewaveguide element, and the degree of expansion or contraction ofwaveguide element can be decreased.

[0045] The invention according to claim 12 relates to the opticalwaveguide device of claim 11, in which the layout pattern of the coarsesurface of the confronting surface is set depending on thetwo-dimensional pattern of the waveguide element.

[0046] Namely, according to the invention of claim 12, imbalance ofexpansion and contraction by temperature with respect to thetwo-dimensional configuration of the optical waveguide device iseliminated or decreased by controlling the layout pattern of the coarsesurface. Herein, the layout pattern of the coarse surface is not themere pattern of the region in which the coarse surface is disposed, butincludes selective use of plural coarse surface patterns showing whichcoarse surface is disposed in which region, or an analog pattern layoutshowing the region of continuous variation of degree of coarseness ofthe coarse surface.

[0047] The invention according to claim 13 is a optical waveguide devicewhich comprises (a) a flat waveguide element composed of a substratelayer and a waveguide layer, (b) a first correction substrate affixed tothe upper side of the waveguide element, having a negative linearexpansion coefficient, and (c) a second correction substrate affixed tothe lower side of the waveguide element, having a negative linearexpansion coefficient.

[0048] Namely, according to the invention of claim 13, since the firstor second correction substrate having a negative thermal expansioncoefficient is affixed to the upper side and lower side of the flatwaveguide element, expansion or contraction of the waveguide element dueto temperature changes can be suppressed. Moreover, since thesecorrection substrates enclose the both sides of the flat waveguideelement, by setting their coefficients of linear expansion or thicknessproperly, warp of the waveguide element can be kept to a minimum limit.

[0049] The invention according to claim 14 relates to the opticalwaveguide device of claim 13, in which the absolute value of the linearexpansion coefficient of the first correction substrate is smaller thanthat of the linear expansion coefficient of the second correctionsubstrate.

[0050] Namely, according to the invention of claim 14, the first andsecond correction substrates are different in the linear expansioncoefficient, and the absolute value of the linear expansion coefficientof the first correction substrate is smaller than that of the linearexpansion coefficient of the second correction substrate, warp of thewaveguide element can be suppressed more efficiently.

[0051] The invention according to claim 15 relates to the opticalwaveguide device of claim 13 or 14, in which the waveguide element andthe first and second correction substrates are affixed with an adhesiveof high rigidity.

[0052] Namely, according to the invention of claim 15, being affixedwith an adhesive of high rigidity, expansion or contraction ofcorrection substrate due to temperature can be efficiently transmittedto the waveguide element, and the degree of expansion or contraction ofwaveguide element can be decreased.

[0053] The principle of the configuration of the invention is explainedbelow.

[0054]FIG. 1 shows an arrayed waveguide grating as a optical waveguidedevice according to the invention. This arrayed waveguide grating 201comprises a waveguide element 203 forming an optical waveguide pattern202, and first and second correction substrates 204, 205 disposed atboth sides to enclose them.

[0055]FIG. 2 shows a sectional structure of the arrayed waveguidegrating in this embodiment. More specifically, the arrayed waveguidegrating 201 comprises the flat waveguide element 203 of specifiedthickness h₀ forming an optical waveguide layer 211 on a siliconsubstrate 212, the first correction substrate 204 of thickness h₁adhered to the optical waveguide layer 211 side, and the secondcorrection substrate 205 of thickness h4 adhered to the siliconsubstrate 212 side. The waveguide element 203 is composed of the opticalwaveguide layer 211 of thickness h₂ and the silicon substrate 212 ofthickness h₃. The optical waveguide layer 211 and first correctionsubstrate 204 are adhered with a first adhesive 214, and the siliconsubstrate 212 and second correction substrate 205 are adhered with asecond adhesive 215.

[0056] The first and second adhesives 214, 215 are different from theadhesive hitherto used for adhering the silicon substrate 212 with othersubstrate, but adhesives of high rigidity are used. Conventionally, inconsideration of prevention of difference in expansion or contractiondue to temperature changes between substrates different in linearexpansion coefficient from being transmitted to other substrates as faras possible, a flexible material of low rigidity was used as theadhesive, but in this embodiment, in order that the effects of expansionor contraction of one substrate may be transmitted to other substrate,the adhesive is selected from a completely opposite point of view.

[0057] The linear expansion coefficient and Young's modulus of eachlayer of the arrayed waveguide grating 201 are defined as follows. Inthe diagram, the linear expansion coefficient of the highest firstcorrection substrate 204 is supposed to be α₁ and its Young's modulus isE₁. The linear expansion coefficient of the optical waveguide layer 211of the optical waveguide element is supposed to be α₂ and its Young'smodulus is E₂. The linear expansion coefficient of the waveguidesubstrate 212 of the optical waveguide element is supposed to be α₃ andits Young's modulus is E₃. The linear expansion coefficient of thesecond correction substrate 205 is supposed to be α₄ and its Young'smodulus is E₄. Generally, the optical waveguide layer 211 of the opticalwaveguide element is extremely thin as compared with other parts such asthe first correction substrate 204, silicon substrate 212 and secondcorrection substrate 205. Namely, the thicknesses h₁, h₂, h₃, h₄ are inthe following relation.

h₂<<h₁, h₃, h₄

[0058] Herein, the linear expansion coefficient α shows the degree ofexpansion or contraction of the substance itself by heat, and it isassumed that the both ends are open. The stress may be expressed as theproduct of Young's modulus multiplied by the distortion. The greater theYoung's modulus, the stronger becomes the tensile stress due toexpansion or contraction. Or, the greater the thickness h₁ to h₄ of thesubstrates, the stronger is the force of pulling or compressing theother substrate at the time of expansion or contraction.

[0059] Prior to analysis of the structure of optical waveguide element203 shown in FIG. 2 enclosed by the first and second correctionsubstrates 204, 205 from above and beneath, first, a structure ofindependent presence of the waveguide element 203, that is, thestructure in the absence of the first and second correction substrates204, 205 is explained. The waveguide element 203 is composed by formingthe optical waveguide layer 211 on the silicon substrate 212 asmentioned above. Such substrate composed of two adhered layers is calleda “two-layer adhered structure” in this specification.

[0060]FIG. 3 shows before and after the change when the waveguideelement is elongated in the waveguide direction due to temperature rise.FIG. 3(a) shows a state before elongation, and FIG. 3(b) shows anelongated state. In the diagram, reference numeral 231 shows theposition of the waveguide, and it is disposed in the optical waveguidelayer 211 in the direction of arrow 232. Since the optical waveguidelayer 211 and silicon substrate 212 have different coefficients oflinear expansion α₁, α₂, when the temperature changes, the entirewaveguide element 203 is warped as shown in FIG. 3(b).

[0061]FIG. 4 shows the dislocation of wavelength due to TE polarizationand TM polarization caused by such warping. In FIG. 4(a), acharacteristic curve 241 of TE polarization and a characteristic curve242 of TM polarization coincide nearly with each other, but as a resultof warping, these characteristic curves 241, 242 differ as shown in FIG.4(b). Thus, in order to avoid or lessen such temperature dependence, itis necessary to prevent or decrease occurrence of warp due totemperature rise.

[0062] Incidentally, considering the vertical relation of the opticalwaveguide layer 211 formed on the silicon substrate 212 of the waveguideelement 203, the “two-layer adhered structure” is realized in two modes,that is, concave warping and convex warping due to temperature rise. Ofcourse, in the case of concave warping S due to temperature rise, it isconvex warping at the time of temperature fall, and in the case ofconvex warping due to temperature rise, it is concave warping at thetime of temperature fall. Warping of the two-layer adhered structure isdiscussed in each case.

[0063] (1) Concave warping of “two-layer adhered structure” due totemperature rise

[0064] In this case, the linear expansion coefficient α₃ is greater thanthe linear expansion coefficient α₂ in FIG. 2. It is expressed informula (3-1-1).

α₂<α₃ (however, α₂>0)   (3-1-1)

[0065] (2) Convex warping of “two-layer adhered structure” due totemperature rise

[0066] In this case, the linear expansion coefficient α₂ is greater thanthe linear expansion coefficient α₃ in FIG. 2. It is expressed informula (3-2-1).

α₂>α₃ (however, α₃>0)   (3-2-1)

[0067] (3) No warping of “two-layer adhered structure” due totemperature rise

[0068] In this case, the linear expansion coefficient α₃ and the linearexpansion coefficient α₂ are equal to each other in FIG. 2. It isexpressed in formula (3-3-1).

α₂=α₃   (3-3-1)

[0069] Suppose the “two-layer adhered structure” is combined with thefirst correction substrate 204 and second correction substrate 205 aboveand beneath as shown in FIG. 2. Similarly, each case is discussed.Herein, the optical waveguide device is supposed to be a thermal, thatis, the temperature dependence is decreased

[0070] (4) concave warping of “two-layer adhered structure” due totemperature rise (convex warping due to temperature fall)

[0071] In this case, the “two-layer adhered structure” is warped in aconcave profile due to temperature rise in the condition of formula(3-4-1).

α₂<α₃ (however, α₂>0)   (3-4-1)

[0072] To decrease elongation and warp of the optical waveguide element203, when the first correction substrate 204 and second correctionsubstrate 205 are disposed as shown in FIG. 2, the first correctionsubstrate 204 and second correction substrate 205 must have, ifpositive, a sufficiently small (close to zero) value of linear expansioncoefficient (3-4-2), or a negative linear expansion coefficient (3-4-3)in order to enhance the effect. Accordingly, the elongation of theoptical waveguide element 203 due to temperature rise can be decreased.Further, since the linear expansion coefficient α₄ of the secondcorrection substrate 205 is smaller than the linear expansioncoefficient α₁ of the first correction substrate 204 (in the negativesign, the absolute value is greater), the warp of the optical waveguideelement 203 due to temperature rise can be decreased (3-4-4).

α₁, α₄<α₂   (3-4-2)

α₁, α₄<0   (3-4-3)

α₁>α₄   (3-4-4)

[0073] Next, considering other material characteristics of thecorrection substrate, as shown in the following formulas, the greaterthe Young's modulus, the higher is the rigidity and the smaller is thedistortion in relation to the stress, and the greater the thickness h ofthe substrate, the smaller becomes the distortion. Accordingly, ifformula (3-4-4) is not established, in addition to formula (3-4-2) orformula (3-4-3). when the following formula (3-4-5) or (3-4-6) isestablished, warping of the optical waveguide element 203 due totemperature rise can be decreased. When all formulas (3-4-3), (3-4-4),(3-4-5), and (3-4-6) are satisfied, the greatest effects are obtained,but by increasing the difference of each inequality sign, if the numberof satisfied formulas is small, enough effect to decrease the warping isobtained.

ε=σ/E

[0074] ε: strain, σ: bending stress, E: Young's modulus

σ=M/Z

[0075] M: bending moment, Z: modulus of section

Z=⅙bh²

[0076] b: sectional length of substrate, h: sectional thickness ofsubstrate

E₁<E₄ (however, E₂, E₃<E₄)   (3-4-5)

h₁<h₄ (however, h₂, h₃<h₄)   (3-4-6)

[0077] (5) Convex warping of “two-layer adhered structure” due totemperature rise (concave warping due to temperature fall)

[0078] In this case, the “two-layer adhered structure” is warped in aconvex profile due to temperature rise in the condition of formula(3-5-1).

α₂>α₃ (however, α₃>0)   (3-5-1)

[0079] To decrease elongation and warp of the optical waveguide element203, when the first correction substrate 204 and second correctionsubstrate 205 are disposed as shown in FIG. 2, the first correctionsubstrate 204 and second correction substrate 205 must have, ifpositive, a sufficiently small (close to zero) value of linear expansioncoefficient (3-5-2), or a negative linear expansion coefficient (3-5-3)in order to enhance the effect. Accordingly, the elongation of theoptical waveguide element 203 due to temperature rise can be decreased.Further, since the linear expansion coefficient α₁ of the firstcorrection substrate 204 is smaller than the linear expansioncoefficient α₄ of the second correction substrate 205 (in the negativesign, the absolute value is greater), the warp of the optical waveguideelement 203 due to temperature rise can be decreased (3-5-4).

α₁, α₄<α₂   (3-5-2)

α₁, α₄<0   (3-5-3)

α₄>α₁   (3-5-4)

[0080] Other material characteristics of the correction substrate can beconsidered in the same concept as in the case (4) above, and theexplanation is omitted herein.

[0081] (6) No warping of “two-layer adhered structure” due totemperature changes

[0082] In this case, if the waveguide element 203 for composing thetwo-layer adhered structure is not warped, when the second correctionsubstrate 205 shown in FIG. 2 is affixed to the waveguide substrate 212side in order to support it, as far as its linear expansion coefficientα4 is not equal to the other coefficients of linear expansion α₂, α₃,the entire structure acts to cause convex or concave warping. To preventthis, it is necessary to affix the first correction substrate 204 oflinear expansion coefficient α₁ equal to the linear expansioncoefficient α₄ of the second correction substrate 205 to the opticalwaveguide layer 211 side.

[0083] In an example of the optical waveguide device of the invention,specific values are calculated below.

[0084] As the preliminary condition for calculation, the opticalwaveguide is supposed to be the arrayed waveguide grating 201 shown inFIG. 2. In this arrayed waveguide grating 201, the thickness h₀ of theoptical waveguide element 203 is supposed to be t₁, and the linearexpansion coefficient is α₀. In the first and second correctionsubstrates 204, 205, the thicknesses h₁, h₄ are supposed to be equalvalue t₂, and the coefficients of linear expansion are also supposed tobe equal value α₁. For the sake of simplicity, further, the Young'smodulus of each layer is also assumed to be equal. In this case, theentire linear expansion coefficient α_(all) of the arrayed waveguidegrating 201 is expressed in formula (4). $\begin{matrix}{\alpha_{all} = \frac{{t_{1} \times \alpha_{0}} + {2 \times t_{2} \times \alpha_{1}}}{t_{1} + {2 \times t_{2}}}} & (4)\end{matrix}$

[0085] First, the central wavelength λ0 is set in formula (1), and it isput in formula (2) to be converted into the linear expansion coefficientα, then from its value and formula (4), the coefficients of linearexpansion α₀, α₁, and thicknesses t₁, t₂ of the substrates 203, 204(205) are determined. For example, in the case of a quartz opticalwaveguide element formed on a Si substrate used as the arrayed waveguidegrating 201, these values are calculated.

[0086] The thickness of the Si substrate as the optical waveguideelement 203 is 0.8 mm, and its linear expansion coefficient α₀ is26.3×10⁻⁷/° C. In formula (2), dn_(eq)/dT is 6.0×10⁻⁶, and theequivalent refractive index n_(eq) is 1.46. At the central wavelength α₀of 1.55 μm, suppose to make the temperature dependence zero. Fromformula (1) and formula (2), it is required to satisfy the followingformula (5). $\begin{matrix}{\frac{n_{eq}}{T} + {n_{eq}\alpha_{all}}} & (5)\end{matrix}$

[0087] Therefore, from formula (4), the linear expansion coefficientα_(all) is determined as shown in formula (6).

α_(all)=−41.0×10⁻⁷   (6)

[0088] Suppose the thickness of the first and second correctionsubstrates 204, 205 adhered to the upper and lower side of the opticalwaveguide element 203 to be 1.5 mm. In this case, the linear expansioncoefficient α₁ of the first and second correction substrates 204, 205 isdetermined from formula (4) as shown in the following formula (7).

α₁=−59.0×10⁻⁷   (7)

[0089] It is hence known that the material having such linear expansioncoefficient α₁ should be used as the first and second correctionsubstrates 204, 205.

BRIEF DESCRIPTION OF THE DRAWINGS

[0090]FIG. 1 is a perspective view of an arrayed waveguide grating as anexample of an optical waveguide of the invention.

[0091]FIG. 2 is a sectional view showing an example of section of thearrayed waveguide grating of the invention.

[0092]FIG. 3 shows a modified example of waveguide having effects onpolarization dependence depending on temperature changes.

[0093]FIG. 4 is a diagram showing temperature characteristics ofpolarization dependence occurring when warping as shown in FIG. 3.

[0094]FIG. 5 is a characteristic diagram comparing the centralwavelength temperature characteristic of the arrayed waveguide gratingof the embodiment with an ordinary arrayed waveguide grating.

[0095]FIG. 6 is a characteristic diagram showing the difference ofcentral wavelength between TM polarization and TE polarization due totemperature changes in the arrayed waveguide grating of the embodiment.

[0096]FIG. 7 is a characteristic diagram showing the difference of crestvalue of central wavelength between TM polarization and TE polarizationdue to temperature changes in the arrayed waveguide grating of theembodiment.

[0097]FIG. 8 is a perspective view of arrayed waveguide grating in afirst modified example of the invention.

[0098]FIG. 9 is a sectional view of the arrayed waveguide grating in thefirst modified example.

[0099]FIG. 10 is a sectional view showing an example of the section ofan arrayed waveguide grating in a second modified example of theinvention.

[0100]FIG. 11 is a one-dimensional plan view of a conventionallyproposed optical waveguide element substrate.

[0101]FIG. 12 is a sectional view cutting off the optical waveguideelement substrate shown in FIG. 11 in the longitudinal direction.

[0102]FIG. 13 is a two-dimensional plan view of a conventionallyproposed optical waveguide element substrate.

[0103]FIG. 14 is a side view of the optical waveguide element substrateshown in FIG. 13.

[0104]FIG. 15 is a characteristic diagram comparing a bimetal structureof adhering plate materials different in linear expansion coefficient tothe optical wavelength element substrate shown in FIG. 13 and a case notusing such plate materials.

[0105]FIG. 16 is an essential perspective view of waveguide substrateand aluminum plate adhered thereto.

[0106]FIG. 17 is an essential perspective view showing a processed statefor eliminating distortion of the waveguide substrate and aluminum plateshown in FIG. 16.

[0107]FIG. 18 is a perspective view showing essential parts of a opticalwaveguide device proposing adhesion of a substrate having a negativelinear expansion coefficient to the optical waveguide element.

[0108]FIG. 19 is a perspective view showing other proposal of adhesionof a substrate having a negative linear expansion coefficient to theoptical waveguide element.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments

[0109] As an embodiment, an optical waveguide, a optical waveguidedevice using the same, and a manufacturing method of optical waveguidedevice are explained below. First, as an example of optical waveguide,an arrayed waveguide grating having the configuration as shown in FIG. 1was fabricated. As the preliminary condition, same as shown in FIG. 2,the thickness of the optical waveguide element 203 in the arrayedwaveguide grating 201 is h₀, and the linear expansion coefficient is α₀.Further, the thicknesses of the first and second correction substrates204, 205 are h₁, h₄ are equal value t1, and their coefficients of linearexpansion are equal value α₁. As the first and second correctionsubstrates 204, 205, using glass ceramic, an AWG (arrayed waveguidegrating) variable in temperature dependence was manufactured. Thecoefficients of linear expansion α₁ of the first and second correctionsubstrates 204, 205 are both −6.5×10⁻⁷/° C., and their thickness is 1mm. The linear expansion coefficient α₀ of the optical waveguide element203 is 26.3×10⁻⁷/° C., and its thickness is 0.8 mm.

[0110] Using formula (4), the linear expansion coefficient α_(all) ofthe entire arrayed waveguide grating 201 is 2.87×10⁻⁷/° C. Putting it informula (1) and formula (3), the central wavelength temperaturecharacteristic can be determined.

[0111]FIG. 5 compares the central wavelength temperature characteristicof the arrayed waveguide grating of the embodiment with an ordinaryarrayed waveguide grating. In the actually manufactured array waveguidediffraction grating 201, measured results are shown by thecharacteristic curve 301 by plotting each measured value, and a thinline 302 shows the theoretical value. A broken line 303 shows themeasured value of the ordinary arrayed waveguide grating usedconventionally.

[0112] As known from the diagram, the arrayed waveguide grating 201 ofthe embodiment is lowered in the temperature dependence to about 75%(25% down) as compared with the conventional arrayed waveguide gratingindicated by broken line 303. The measured results of the temperaturecharacteristics are slightly different from the theoretical value, whichis considered to be due to error of linear expansion coefficient α,error in the thickness of the optical waveguide element 203 and firstand second correction substrates 204, 205, and absorption of expansionand contraction of mutual substrates by the substrate adhesive layer.

[0113]FIG. 6 and FIG. 7 show evaluation of the polarization dependenttemperature characteristic. Specifically, in FIG. 6, the difference ofcentral wavelength between TM polarization and TE polarization isdenoted on the axis of ordinates, and temperature changes are plotted onthe axis of abscissas. When the arrayed waveguide grating 201 of theembodiment is dependent on temperature, the difference of centralwavelength between TM polarization and TE polarization is expanded orchanged due to temperature rise or the like. However, as clear from FIG.6, if the temperature changes, the difference of the central wavelengthbetween TM polarization and TE polarization is only slightly increasedor decreased within the error range from the center of “zero” level.

[0114] In FIG. 7, the difference of peak value of central wavelengthbetween TM polarization and TE polarization is denoted on the axis ofordinates, and temperature changes are plotted on the axis of abscissas.Namely, as compared with FIG. 6 which shows the change in the deviation.of TM polarization and TE polarization in the lateral direction(wavelength direction) due to temperature of two waveform crests. FIG. 7shows the change in the deviation due to temperature in the longitudinaldirection (crest value direction) of the waveform crests. In FIG. 7,too, the difference between TM polarization and TE polarization is onlyslightly increased or decreased within the error range from the centerof “zero” level. Hence the arrayed waveguide grating 201 of theembodiment is proved to be capable of holding a stable characteristicfree from temperature dependence, without requiring any particulartemperature adjustment for change in the ambient temperature.

[0115] First Modified Example of the Invention

[0116] In the embodiment explained above, the correction substrates aredisposed at both sides of the optical waveguide element 203, but,alternatively, a plurality of two or more correction substrates may bedisposed at one side, and warping may be prevented by them, or theoptical waveguide element 203 itself may be lessened in expansion orcontraction due to temperature. It is also possible to dispose aplurality of correction substrates in a same number or in differentnumbers each at both sides of the optical waveguide element 203.

[0117]FIG. 8 shows an example of arrayed waveguide grating as a opticalwaveguide device in a first modified example of the invention. In thediagram, same parts as in FIG. 1 are identified with same referencenumerals, and their explanation is properly omitted. An arrayedwaveguide grating 401 of the modified example has a second correctionsubstrate 205 adhered to the silicon substrate side of an opticalwaveguide element 203, and also has a first correction substrate 402adhered further beneath it.

[0118]FIG. 9 is a sectional view of the arrayed waveguide grating inthis modified example. The arrayed waveguide grating 401 comprises aflat waveguide element 203 having a specified thickness h₀ forming anoptical waveguide layer 211 on a silicon substrate 212, a secondcorrection substrate 205 of thickness h₄ adhered to this siliconsubstrate 212 side, and a first correction substrate 402 of thickness h₁adhered to other side (lower side in the diagram) of the secondcorrection substrate 205. The waveguide element 203 ₃ is composed of theoptical waveguide layer 211 of thickness h₂ and the silicon substrate212 of thickness h₃. The silicon substrate 212 and second correctionsubstrate 205 are adhered with a second adhesive 215, and the secondcorrection substrate 205 and first correction substrate 402 are adheredwith a first adhesive 411. The first and second adhesives 411, 215 arehigh in rigidity same as in the foregoing embodiment.

[0119] In the arrayed waveguide grating 401 of the modified example, thecoefficients of linear expansion α₁, α₄, and Young's moduli E₁, E₄ areset so as to decrease the warp caused when only the waveguide element203 and second correction substrate 205 are adhered, and expansion andcontraction due to temperature changes of the waveguide element 203,sufficiently by the first correction substrate 402.

[0120] Second Modified Example of the Invention

[0121]FIG. 10 shows a sectional structure of an arrayed waveguidegrating in a second modified example of the invention. In the diagram,same parts as in FIG. 2 are identified with same reference numerals, andtheir explanation is properly omitted.

[0122] In an arrayed waveguide grating 201A of the modified example,mutual confronting surfaces of a first correction substrate 204A andoptical waveguide layer 211A of waveguide element 203A are processed ina coarse surface having fine undulations. Similarly, mutual confrontingsurfaces of a silicon substrate 201A of the waveguide element 203A and asecond correction substrate 205A are processed in a coarse surfacehaving fine undulations. A first adhesive 501 for adhering the firstcorrection substrate 204A and optical waveguide layer 211A, and a secondadhesive 502 for adhering the silicon substrate 212A and secondcorrection substrate 205A are not particularly high in rigidity afteradhesion, but are ordinary adhesives as usually hitherto.

[0123] Namely, in the arrayed waveguide grating 201A of the secondmodified example, since expansion or contraction due to temperature ofthe first correction substrate 204A and second correction substrate 205Ais transmitted to the waveguide element 203A side through the mutuallycoarse surfaces of the contact surfaces, warping can be preventedeffectively without requiring the first and second adhesives 501, 502 ofparticularly high rigidity. Of course, the coarse surface may be onlyone of the confronting surfaces. Such processing may be done on one ofthe confronting surfaces of the first correction substrate 204 andsecond correction substrate 205, and other confronting surface may beprocessed with a special adhesive as explained in the foregoingembodiment.

[0124] Moreover, the pattern of coarse surface may be properly designed.Herein, the layout pattern of coarse surface is not intended to limitthe region of the coarse surfaces to a part of the confronting surfaces,but includes selective use of plural coarse patterns for disposing whichcoarse surface in each region, or an analog pattern layout showing theregion of continuous variation of the degree of coarse surface.

[0125] In the foregoing embodiment and modified examples, the arrayedwaveguide gratings 201, 401 are explained, but the invention may beapplied to other waveguide elements such as Mach-Zehnder interferometer.

[0126] As described herein, according to the invention of claims 1 to15, in order to eliminate the temperature dependence of opticalcharacteristics of the conventional optical waveguide element, andsuppress the thermal deformation of the waveguide element in thelongitudinal direction, the linear expansion coefficient is differentfrom the case of adhering a correction plate smaller than the waveguideelement, correction substrates are disposed at both sides of thewaveguide element, and these material characteristics (linear expansioncoefficient, Young's modulus, thickness, etc.) are taken intoconsideration, and the thermal deformation in the warping direction canbe suppressed. Hence it can solve the conventional problems ofdeterioration of other optical characteristics of waveguide element dueto thermal deformation in the warping direction.

[0127] According to the invention of claim 1, plural flat correctionsubstrates are affixed to both sides or one side of the flat waveguideelement, and all of them including the waveguide element are set to suchvalues that their length and warping force due to temperature changesmay be decreased as compared with the case of the waveguide elementalone. For example, when one correction substrate is affixed to one sideof the waveguide element, warping may occur on the whole due todifference in the linear expansion coefficient of the waveguide element,but this warping can be decreased by affixing further one or a pluralityof correction substrates to this correction substrate and setting thecoefficients of linear expansion of these correction substrates atproper values. Moreover, by correcting the direction of suppressing theexpansion or contraction due to temperature of the waveguide element bythese correction substrates, fluctuations of characteristics of thewaveguide element can be suppressed if temperature changes occur, sothat temperature adjustment of waveguide element may not be required.Hence, the cost is lowered and the electric power is saved,

[0128] According to the invention of claim 2, first and secondcorrection substrates are affixed so as to enclose at both sides of theflat waveguide element, and the coefficients of linear expansion of thefirst and second correction substrates are set to such values that thelength and warping force of the waveguide element due to temperaturechanges may be decreased as compared with the case of the waveguideelement alone. Therefore, warping of waveguide element at varioustemperatures can be decreased, and fluctuation of characteristics of thewaveguide element can be suppressed. Besides, temperature adjustment ofwaveguide element is not required, and hence the device cost is loweredand the electric power is saved.

[0129] According to the invention of claim 3, first and secondcorrection substrates are affixed so as to enclose at both sides of theflat waveguide element, and the coefficients of linear expansion of thefirst and second correction substrates, or Young's moduli, orthicknesses, or plural items thereof set at such values as to decreasethe length and warping force of the waveguide element due to temperaturechanges as compared with the case of the waveguide element alone.Warping of the waveguide element can be decreased effectively. Moreover,by correcting in the direction of suppressing the expansion orcontraction due to temperature of the waveguide element by the first andsecond correction substrates, fluctuations of characteristics of thewaveguide element can be suppressed if temperature changes occur, sothat temperature adjustment of waveguide element may not be required.

[0130] According to the invention of claim 4, first and secondcorrection substrates are affixed so as to enclose at both sides of theflat waveguide element. Herein, the second correction substrate isdisposed at the substrate side of the waveguide element, and is thickerthan the first correction substrate, and has a linear expansioncoefficient smaller than the linear expansion coefficient of thewaveguide element, and a linear expansion coefficient smaller than thelinear expansion coefficient of the first correction substrate. Sincethe first and second correction substrates have a thickness greater thanthe thickness of the waveguide element and a linear expansioncoefficient smaller than the linear expansion coefficient of thewaveguide element, expansion or contraction of the waveguide element dueto temperature changes can be suppressed. Moreover, since thesecorrection substrates are enclosing the both sides of the waveguideelement, by properly setting their coefficients of linear expansion orthickness, generation of warp of waveguide element can be suppressed toa minimum limit. In the invention of claim 4, still more, since thefirst and second correction substrates differ in the linear expansioncoefficient and the first correction substrate has a greater negativevalue, the first correction substrate disposed at the waveguide layerside of the waveguide element can be formed relatively in a smallerthickness. In addition, by the first and second correction substrates,expansion and contraction of the waveguide element due to temperaturecan be corrected in a suppressing direction, and fluctuations ofcharacteristics of the waveguide element can be suppressed iftemperature changes occur, so that temperature adjustment of waveguideelement may not be required.

[0131] According to the invention of claim 5, first and secondcorrection substrates are affixed so as to enclose at both sides of theflat waveguide element Herein, the first correction substrate isdisposed at the substrate side of the waveguide element, and is thickerthan the waveguide element, and has a negative linear expansioncoefficient. The second correction substrate is disposed at thesubstrate side of the waveguide element, and is thicker than the firstcorrection substrate, and has a negative linear expansion coefficient,and more specifically has a linear expansion coefficient of a greaterabsolute value than the linear expansion coefficient of the firstcorrection substrate. Since the first and second correction substrateshave a thickness greater than the thickness of the waveguide element anda negative linear expansion coefficient, expansion or contraction of thewaveguide element due to temperature changes can be suppressed.Moreover, since these correction substrates are enclosing the both sidesof the waveguide element, by properly setting their coefficients oflinear expansion or thickness, generation of warp of waveguide elementcan be suppressed to a minimum limit, In the invention of claim 5, stillmore, since the second correction substrate has a linear expansioncoefficient of a larger absolute value than the linear expansioncoefficient of the first correction substrate, the first correctionsubstrate disposed at the waveguide layer side of the waveguide elementcan be formed relatively in a smaller thickness. In addition, by thefirst and second correction substrates, expansion and contraction of thewaveguide element due to temperature can be corrected in a suppressingdirection, and fluctuations of characteristics of the waveguide elementcan be suppressed if temperature changes occur, so that temperatureadjustment of waveguide element may not be required.

[0132] According to the invention of claim 6, in the optical waveguidedevice of any one of claims 2 to 5, one of the first and secondcorrection substrates can be shared by the holding plate of thewaveguide element. Hence, the entire size of the optical waveguidedevice is suppressed, which contributes to reduction of cost.

[0133] According to the invention of claim 7, in the optical waveguidedevice of claim 3, the first and second correction substrates aremutually equal in the linear expansion coefficient and Young's modulus,and mutually equal in thickness. Therefore, parts can be commonly used,and the cost of the parts can be curtailed.

[0134] According to the invention of claim 8, in the optical waveguidedevice of any one of claims 1 to 5, the waveguide element and correctionsubstrate are affixed with an adhesive of high rigidity, expansion orcontraction of correction substrate due to temperature can beefficiently transmitted to the waveguide element, and absorption ofstress due to deformation of adhesive layer can be curtailed.

[0135] According to the invention of claim 9, the optical waveguidedevice has a clamp glass, and the adhesion strength of the fiber arraycan be reinforced.

[0136] According to the invention of claim 10, in the optical waveguidedevice of claim 9, the first correction substrate is as thin as theclamp glass or less, and the thickness of the entire device is notparticularly increased.

[0137] According to the invention of claim 11, since at least a part ofthe confronting sides of the waveguide element and correction substrateis a coarse surface, expansion or contraction of correction substratedue to temperature can be efficiently transmitted to the waveguideelement, and the degree of expansion or contraction of waveguide elementcan be decreased. Moreover, the range of selection of adhesive isexpanded.

[0138] According to the invention of claim 12, imbalance of expansionand contraction by temperature with respect to the two-dimensionalconfiguration of the optical waveguide device is eliminated or decreasedby controlling the layout pattern of the coarse surface. Herein, if theoptical waveguide device has a complicated shape two-dimensionally, itsexpansion or contraction can be corrected at high precision.

[0139] According to the invention of claim 13, since the first or secondcorrection substrate having a negative thermal expansion coefficient isaffixed to the upper side and lower side of the flat waveguide element,expansion or contraction of the waveguide element due to temperaturechanges can be suppressed. Moreover, since these correction substratesenclose the both sides of the flat waveguide element, by setting theircoefficients of linear expansion or thickness properly, warp of thewaveguide element can be kept to minimum.

[0140] According to the invention of claim 14, the first and secondcorrection substrates are different in the linear expansion coefficient,and the absolute value of the linear expansion coefficient of the firstcorrection substrate is smaller than that of the linear expansioncoefficient of the second correction substrate, so that the firstcorrection substrate disposed at the waveguide layer side of thewaveguide element may be relatively thin.

[0141] According to the invention of claim 15, being affixed with anadhesive of high rigidity, expansion or contraction of correctionsubstrate due to temperature can be efficiently transmitted to thewaveguide element, and the degree of expansion or contraction ofwaveguide element can be decreased.

[0142] Although the invention has been described with respect tospecific embodiment for complete and clear disclosure, the appendedclaims are not to be thus limited but are to be construed as embodyingall modification and alternative constructions that may be occurred toone skilled in the art which fairly fall within the basic teachingherein set forth.

What is claimed is:
 1. A optical waveguide device comprising: a flatwaveguide element having a specified thickness with a waveguide layerformed on a substrate, and a correction substrate made of a plurality offlat materials affixed to both sides or one side of the waveguideelement, for decreasing the length and warping force of the waveguideelement due to temperature changes as compared with the case of thewaveguide element alone.
 2. A optical waveguide device comprising: aflat waveguide element having a specified thickness with a waveguidelayer formed on a substrate, and first and second correction substratesmade of two flat materials affixed to both sides of the waveguideelement, having their coefficients of linear expansion set at suchvalues as to decrease the length and warping force of the waveguideelement due to temperature changes as compared with the case of thewaveguide element alone.
 3. A optical waveguide device comprising: aflat waveguide element having a specified thickness with a waveguidelayer formed on a substrate, and first and second correction substratesmade of two flat materials affixed to both sides of the waveguideelement, having their coefficients of linear expansion, or moduli oflongitudinal elasticity, or thicknesses, or plural items thereof set atsuch values as to decrease the length and warping force of the waveguideelement due to temperature changes as compared with the case of thewaveguide element alone.
 4. A optical waveguide device comprising: aflat waveguide element having a specified thickness with a waveguidelayer formed on a substrate, a first correction substrate disposed atthe waveguide layer side of this waveguide element, having a thicknessgreater than the thickness of the waveguide element and a linearexpansion coefficient smaller than the linear expansion coefficient ofthe waveguide element, and a second correction substrate disposed at thesubstrate side of the waveguide element, thicker than the firstcorrection substrate, and having a linear expansion coefficient smallerthan the linear expansion coefficient of the waveguide element, and alinear expansion coefficient smaller than the linear expansioncoefficient of the first correction substrate.
 5. A optical waveguidedevice comprising: a flat waveguide element having a specified thicknesswith a waveguide layer formed on a substrate, a first correctionsubstrate disposed at the waveguide layer side of this waveguideelement, having a thickness greater than the thickness of the waveguideelement and a negative linear expansion coefficient, and a secondcorrection substrate disposed at the substrate side of the waveguideelement, thicker than the first correction substrate, and having anegative linear expansion coefficient, and a linear expansioncoefficient of greater absolute value than the linear expansioncoefficient of the first correction substrate.
 6. The optical waveguidedevice of any one of claims 2 to 5, wherein one of the first and secondcorrection substrates is a plate for holding the waveguide element. 7.The optical waveguide device according to claim 3, wherein the first andsecond correction substrates are mutually equal in the linear expansioncoefficient and modulus of longitudinal elasticity, and also mutuallyequal in the thickness.
 8. The optical waveguide device of any one ofclaims 1 to 5, wherein the waveguide element and the correctionsubstrate are affixed to each other with an adhesive of high rigidity.9. The optical waveguide device of any one of claims 1 to 5, furthercomprising: a fiber array for coupling optically with the waveguideelement, and a clamp glass disposed at the upper side of the waveguideelement for reinforcing the adhesive strength of the fiber array. 10.The optical waveguide device according to claim 9, wherein the thicknessof the first correction substrate is equal to or smaller than that ofthe clamp glass.
 11. The optical waveguide device of any one of claims 1to 5, wherein at least one of the confronting surfaces of the waveguideelement and correction substrate is a course surface.
 12. The opticalwaveguide device according to claim 11, wherein the layout pattern ofthe coarse surface of the confronting surface is set depending on thetwo-dimensional pattern of the waveguide element
 13. A optical waveguidedevice comprising: a flat waveguide element composed of a substratelayer and a waveguide layer, a first correction substrate affixed to theupper side of the waveguide element, having a negative linear expansioncoefficient, and a second correction substrate affixed to the lower sideof the waveguide element, having a negative linear expansioncoefficient.
 14. The optical waveguide device of claim 13, wherein theabsolute value of the linear expansion coefficient of the firstcorrection substrate is smaller than that of the linear expansioncoefficient of the second correction substrate.
 15. The opticalwaveguide device of claim 13 or 14, wherein the waveguide element andthe first and second correction substrates are affixed with an adhesiveof high rigidity.